This invention is intended for use in traditional telephone networks that carry voice, facsimile or voice-band-data (VBD) traffic. The term "facsimile" represents Group 3 facsimile, which is a ubiquitous international standard for communicating facsimiles of documents over telephone networks. The term "voice-band-data" represents machine-generated information transported over a standard telecommunications voice channel. While facsimile is a form of voice-band-data, it is mentioned separately in this document to highlight the fact that it may be separately classified in the invention.
There is a need for telecommunications service providers to perform policing functions for prevention of fraudulent use of telephone services. As noted by Else and Frantzen in U.S. Pat. No. 4,811,378, fraud prevention is an ongoing challenge for telecommunications service providers: an industry has flourished to develop methods and devices for evasion of billing. Many such devices rely on the fact that most of today's telecommunications switches open a communications channel as soon as a call is placed, even though billing does not start until the network establishes that the call has been answered. As a consequence, the answering party can evade billing by using a device that withholds the answer supervision response, which is the signal that indicates that the call has been answered.
Customers with 1-800 numbers have a strong motivation to evade billing through suppression of the answer supervision response because they both answer the call and receive the bill. Such customers usually have the means to evade billing as well, as they generally operate telephone switching equipment called private-branch exchanges (PBXs) which can be configured to suppress the answer supervision response.
Suitable approaches for control of answer supervision fraud are as follows:
1. Switches in the telephone network could be upgraded in accordance with U.S. Pat. No. 4,811,378 such that an open talk channel is only provided after the answer supervision response is observed. Such an upgrade is extremely expensive and time-consuming. Furthermore, one has the technical challenge of ensuring that customers hear each other soon as the call is answered, which is the reason that most switches were designed to provide an open talk channel during call setup. PA1 2. A device such as is described in U.S. Pat. No. 4,811,378 could be inserted into the network so as to block one side of the communications channel until the answer supervision response is observed. Such a device interferes in the normal functioning of the network for all calls, only a small minority of which are fraudulent. Means must be incorporated into the network to promptly disable the device when the call is answered, and to override the device when required for network maintenance and administration. Furthermore, such a device will block service usage by honest customers when the answer supervision response is missed because of equipment failure within the network. PA1 3. Intervention could be imposed when a call remains unanswered for an inordinate period of time. The intervention may be to terminate the call or to insert the missing answer supervision response. Unfortunately, the time-out period for this approach needs to be quite long because honest customers may wait a significant period of time for a call to be answered. Also, failure to produce an answer supervision response can be due to faults in the network equipment, and it is not desirable to disturb honest customers when such is the case.
There is a need for telecommunications service providers to regulate access to specialized telephone services which depend on the manner of customers' use. Such a function is performed by a predecessor to the present invention, herein called the FaxCom device.sup.1. The FaxCom device was deployed across Canada in 1990 to support a reduced-rate facsimile-and-data-only service called FaxCom. It has also been demonstrated and sold to various international clients since 1990, and it has been offered as a vehicle for implementing class-based billing, where customers are billed differently based on whether their calls are voice, facsimile or voice-band-data. A general description of the FaxCom device was published in an article by Randall A. Law, Terrence W. Holm and Neil B. Cox entitled "Real-Time Multi-Channel Monitoring of Communications on a T1 Span", published in the Proceedings of the 1991 IEEE Pacific Rim Conference on Communications, Computers and Signal Processing at pages 306 to 309.
The FaxCom device determines whether Voice, Facsimile or VBD are present on designated telephone calls, and imposes a voice message and terminates the call when voice is observed. The FaxCom device only applies policing when both sides of the channel are off-hook, which precludes its use in policing of call setup processes for control of answer supervision fraud. The FaxCom device does not separately classify handshaking signals or audible network signaling, and as a consequence it is unnecessarily slow in detecting Facsimile and VBD. Finally, the FaxCom device is not suitable when the direction of traffic flow is important, as it is not able determine which end of the communications channel is generating traffic.
Other patents include components for classifying telephone signals, such as U.S. Pat. No. 5,539,804, U.S. Pat. No. 4,809,272, U.S. Pat. No. 4,815,137, U.S. Pat. No. 4,815,136 and U.S. Pat. No. 4,720,862. However, none of these other inventions is comprised of a comparable combination of signal classification and source classification for policing of specialized telephone services.
Therefore, there is a need for a system and method to actively determine the properties of customer usage of telephone services, and to promptly implement prescribed actions based on the observed properties. This enables telecommunications service providers to perform policing functions for prevention of fraudulent use of telephone services. This also provides a means for regulating access to specialized telephone services which depend on the manner of customers' use.